Pilot-activated diaphragm-operated valves for use in irrigation systems are known, and a typical example is shown in U.S. Pat. No. 3,336,843. This style of valve has a closure member with a seal which moves against or away from an annular seat to close or open the valve. The closure member is driven by a flexible diaphragm which is normally urged toward a closed position by a spring and by upstream fluid pressure acting against the diaphragm. When the valve is to be opened, the fluid pressure is relieved by bleeding fluid out of the diaphragm chamber through a manual valve or a remotely operated solenoid valve.
In recent years, valves of this type have been made from plastic rather than metal components. Plastic materials (such as PVC) have substantially eliminated the corrosion and mineral-deposit problems which have limited the service life of metal valves, and plastic valves are readily coupled to water lines. Plastic valve seats, however, have not been reliable because the plastic material is too easily scratched, chipped or abraded by sand or small stones in the irrigation water stream, and this damage results in water leakage and a need for frequent maintenance.
Attempts have been made to incorporate a generally cylindrical metal seat ring in a plastic valve body, but the failure rate on these valves is excessive due to an inadequate bond between the ring and plastic which have different thermal expansion properties. Loosening of this style of metal seat can also occur during distortion of the plastic valve body resulting from transient hydraulic shock when the valve is opened and closed. The metal valve-seat ring of this invention solves these problems by enabling economical molded-in construction with a rugged and abrasion-resistant stainless-steel ring which is physically locked into the valve body.